Bifacial silicon heterojunction solar cells using transparent-conductive-oxide- and dopant-free electron-selective contacts

The development of transparent electron-selective contacts for dopant-free carrier-selective crystalline silicon (c-Si) heterojunction (SHJ) solar cells plays an important role in achieving high short-circuit current density (J_SC) and consequently high photoelectric conversion efficiencies (PCEs). This becomes even more important when focusing on the development of bifacial solar cells. In this study, bifacial SHJ solar cells using a transparent-conductive-oxide-free and dopant-free electron-selective passivating contacts are developed, showing a J_SC bifaciality of up to 97%. Intrinsic ZnO_X layer deposited by atomic layer deposition was used in this structure, which simultaneously provides negligible passivation loss after annealing and enables a low contact resistivity on the electron-selective contact. With both side finger metal electrodes contact, this bifacial solar cell shows an efficiency of 21.2% under front-side irradiation and 20.4% under rear-side irradiation, resulting in an estimated output power density of 24.1 mW/cm² when considering rear-side irradiance of 0.15 sun.